Phonic diaphragm



April 12, 1927.

1,624,357 A. M. NICOLSON PHONIC DIAPHRAGM Filed June 15. 1923 Patented Apr, 12, 1927.

UNITED STATES r 1,624,357 PATENT OFFICE;

ALEXANDER x. mcoLson, or NEW YORK, N. Y., ASSIGNOB r wns'rnan nnac rmc COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION 01' NEW-YORK PHONIC DIAPHRAGM.

Application filed 31111:.15, 1923. Serial no. 645,617.

This invention relates to phonic diaphragms, and has for an object to reduce the transition losses which are occasioned by reason of the fact that the motor, the

dia )hragm and the air to which the sound is to radiated, all have different impedances. I

The object is accomplished by providing a special form of diaphragm, preferably a v1o large direct actin diaphragm, so that the im edance of the iaphragm at the point or points to which the motor drive is connect:

' the perip cry, or it may take the form of a conical diaphragm having sections which decrease in density from the apex towards the periphery..,

A further object of the invention is to reduce the transition losses occasioned by the use of a stiff ferrule or the like, connected at thevcenter of a diaphragm, of a mechanically weak material, such aspaper. This is accomplished by reducing the cross section of the ferrule as the periphery is ap roached.

or further details of the invention, reference may be made to the drawings in which 'Fig. 1 is a front elevation of a corrugated diaphragm with a piezo electricdrive therefor. Fig. 2 is a side elevation of Fig. '1. Figs. 3, 4 and 5 are modifications showing diaphragnis having different forms and composed of graduated masses. Fig. 5 also shows the tapering ferrule. I

Referring in detail to Fig. 1, the piezo electrical crystal 1 with the base 2 and driving arm 3 are of the form shown and de scribed in my Patent No. 1,562,578, lssued Nov. 24, 1925. The bar 3 oscillates in accordance with the motion of the diaphragm 4 and sets up corres onding electric waves magnetic, or other form of drive. may be substituted for the piezo drive illustrated.

Through the outwardly projecting end of the bar 3 extends a pin 5 suitably fastened to the end of the diaphragm 4. This pin in all the forms illustrated, scrvcsas a sound supporting means for the diaphragm which may be of the order of a foot or more in diameter and composed of paper or similar material. The diaphragm, therefore, has a vibratile periphery. f

The desired matchin of impcdances is obtained, in the case of Fi s. 1 and 2, by corrugations '(i which taper in size from the apex towards the periphery, so as to provide a maximum impedance at the apex which approximately matches the impedance of the electric drive and so as to provided a minimum impedance at the periphery which approximately matches the impedance of the surrounding air.

Other forms of attenuated peripheries are. illustrated by thecorrugations 7 in Fig. 3,

and by the curves 8 and 9 in Figs. 4 and 5,

respectively. In Fi s. 3, 4 and 5, the diaphragm is compose of graded masses 10, 11 and 12, which decrease in density as the periphery'is approached and which may be obtained in the case of a paper diaphragm by using different numbers of coatings of varnish, shellac, bakelite, or the like.

The'particular form of electric drive illustrated has a high impedance, and it, has been found preferable to use a metal ferrule 13 for making connection between the pin 5 and the diaphragm. This ferrule may be in the form of concentric cones, one placed insideand the other placed outside of the apex of the diaphragm, two cones being held together by nuts threaded on the pin 5, or in any other suitable way. In order to reduce the transition loss between the ferrule 13 and the diaphragm, it is proposed to use a stiffening agency 14 (Fig. 5) placed inside of the cone and which may bemade by forming molten Rochelle salts into the desired shape. The cross section of this stiffener decreases in succession as the periphery is approached, and being connected to both the ferrule and the diaphragm, serves to graduate the impedance.

What is claimed is: i

1. A large direct acting diaphragm having a vibratile periphery, a driving element connected thereto, said diaphragm having a plurality of corrugations therein whereby the impedance of the diaphragm at the point of connection substantially equals the impedance of the driving element, and the impedance of the peripheral portion of the diaphragm is substantially less than at said point of connection.

2. A-phonic diaphragm of general conical form having corrugations tapering in size from the center outward whereby said diaphragm is stiiier at the center than at the periphery, the periphery being free to vibrate.

In combination, a diaphragm freely exposed to the air, a driving motor, means associating said driving motor to the diaphragm at one portion thereof, the effective mass and stiffness of said diaphragm being such that its impedance as seen from the driving motor approximately matches the impedance of the motor. while the impedance of the diaphragm as seen from the air which it drives approxin'iately matches the impedance of the surrounding air.

4. A diaphragm having a vibratile periphery, a drive therefor, means comprising a stifi'ening device for connecting said drive to said dia hragm, said means having a gradually ecreasing mass and stiffness whereby the impedance is graduated in accordance with the distance from said drive.

5. In a large direct acting diaphragm having a vibratile periphery, a small central portion and an outer portion, said central portion bein" of reater density and of higher impedhnce than said outer portion, the edge of the central portion being defined by a lurality of projections tapering progressive y in the direction of the periphery whereby approximately uniform transition is obtained between the portions of different densities.

(i. In a large dir ct acting conical diaphragm having a vibratile periphery, a cen tral portion and an outer portion, said.

central portion being of greater density than said outer portion, the density of said central portion decreasing in the direction of the periphery whereby the transmission losses due to the sections of different densities are reduced to a minimum.

In witness whereof, I hereunto subscribe my name this (3th day of June A. D. 1923.

ALEXANDER M. NICOLSON. 

